Question

7. Consider a triprotic system whose fully protonated form can
be denoted by H3A. By definition, the fractional composition of the
most basic form of the system, A3-, can be written as:

αA3-=
[A3-]/([H3A]+[H2A-]+[HA-]+[A3-])

a) Derive the expression for the fractional composition of the
most basic form of the system, A3-, in terms of [H+] and Ka
s.

b) Based on the expression you get in (a) and the patterns for
alpha fractions, write the expressions for the three remaining α-
fractions of H3A in terms of [H+] and Kas (without going through
the derivations). Note that the denominators of all four
expressions should be the same.

c) Based on the patterns you know, write an equation for the
fractional composition in terms of [H+] and Kas for H2A2− of a
tetraprotic acid H4A. (Again, no derivation is needed.)